What is the part on the left side of the engine compartment in my van?

SKYMOTHA-DUCKINGWALKER

1984 VOLKSWAGEN VAN

200,000 MILES

It looks like an alternator and has a belt connected to it. In my van it is leaking some kind of black stuff that dried and is hard. When I try to crank my engine it makes this loud, whining sound. The van won't start, but it turns over just fine.